Laser package with reversed laser diode

ABSTRACT

A laser package includes a housing and a subassembly to which the critical components of the laser package are mounted. The subassembly is structured to preserve component alignment even in the presence of thermal excursions by ensuring that any movement which might occur effects all the components in a way to preserve alignment. The subassembly is easily removable from the housing and thus permits replacement if a failure should occur. A reverse diode is included to provide a path for reverse currents which otherwise would be damaging to the active laser diode.

FIELD OF THE INVENTION

This invention relates to a laser package and, more particularly, to alow cost laser package which virtually eliminates relative movement ofcritical components and includes a reversed diode for protection fromhandling and operational irregularities.

BACKGROUND OF THE INVENTION

The movement of critical components in a laser package results inmisalignment of, for example, a laser emitting surface and an opticalfiber coupled to it for delivering power to the output of the device.Any misalignment of the emitting surface and the optical fiber reducesoutput power and could result in device failure. Consequently, a greatdeal of attention has been focused on laser mounting and packaging toavoid the effect of thermal excursions which causes such misalignment.

One effort has been directed at providing robust heat sinks for removingheat thus lowering the effects of thermal excursions. Another approachis directed at attaching the fiber to several anchoring points along thelength of the fiber to avoid transmitting stress to the aligned end ofthe fiber abutting the laser emitting surface. In spite of suchapproaches, thermally-induced component movement and the resultingmisalignment remain an ongoing problem in the industry.

Also, a common problem in the industry for laser diodes has been theirsusceptibility to permanent damage followed by a certain failure in anevent of even a small amount of current flow in the reverse directioneither due to handling or due to irregularities in the power supply.Immunity from these kinds of a common problems is assured by the use ofa reverse biased diode.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the principles of this invention, a laser packageincludes a reverse biased diode in addition to a forward biased diode ina removable subassembly with a rigid ceramic surface layer to which thecylindrical lens and the optical fiber end are soldered in properregistration with the emitting surface of the forward biased laser. Anythermal excursions results in the movement of all components in a manerwhich avoids relative movement between them. Thus any misalignment isavoided.

Moreover, the package and the subassembly are relatively easy toassemble and the subassembly is easily removed. Consequently, arelatively low cost, partially-reusable package is achieved with fewerpotential failure modes and thus expected longer lifetimes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are enlarged schematic top and side views of a laserpackage in accordance with the principles of this invention;

FIGS. 3 and 4 are a schematic top view of the subassembly for thepackage of FIGS. 1 and 2 and a pin out portion of that packagerespectively; and

FIGS. 5 and 6 are an enlarged top view of a portion of an alternativesubassembly for the package of FIGS. 1 and 2 and a circuit diagram forthe laser diode arrangement in that alternative subassembly.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT OF THIS INVENTION

FIGS. 1 and 2 show schematic top and side views of a laser package 10 inaccordance with the principles of this invention. The package comprisesfour walls 11, 12, 13, and 14 extending upwards from a floor 15 todefine a housing into which a subassembly 20 is connected by screws 21in FIG. 2. The package includes tubular extension (or output port) 23 inwall 12 to receive an optical fiber 24. Support 29 also is connected tothe floor of the housing by screws as shown.

The subassembly includes a recess 27 into which a laser chip 28 andsupport member 29 fits snugly. A rigid ceramic U-shaped layer 26 issecured about recess 27 on the top surface of the subassembly. Therecess is dimensioned so that the emitting surface of the chip ispositioned at the top surface of the ceramic element facing to theright, as viewed in the figures, so that the energy emitted by theemitting surface of the laser couples into the aligned optical fiber.Member 29 is soldered to subassembly 20 at recess 27 to providestability and rigidity to the package.

FIG. 3 shows an enlarged view of ceramic element 26 encompassing laserchip 28. The figure shows emitting surface 30 of the laser chip coupledinto a cylindrical lens 31 to which end 32 of optical fiber 24 iscoupled in the usual fashion. Cylindrical lens 31 is soldered into placeby means of a solder hybrid comprising resistor pad pairs 35 and 36 and37 and 38 to which voltages are impressed via metallized pads 41 and 42and 43 and 44 correspondingly to heat solder dots positioned between theresistor pad pairs once the cylindrical lens is properly positioned.Such a method of securing a lens is well known and disclosed, forexample, in copending application Ser. No. 8/220,441 filed Mar. 31, 1994for Leslie Rogers and Michael Ung and assigned to the assignee of thepresent application. The end of the optical fiber 24 is secured toceramic element 26 in a similar manner by applying a voltage betweenresistor pad pair 33 and 34 via gold pads 45 and 46. The techniqueemploys platinum, palladium, silver contacts with a resistor formed onan aluminum oxide layer. An impressed current generates heat, via theresistor, which melts the solder dot.

The housing dimensions, the placement of tube 23, the dimensions of thesubassembly, the location of the holes for the screws to secure thesubassembly to the housing, the dimensions of recess 27 and the snug fitof the chip and support in the recess are all maintained withinsufficiently close tolerances so that alignment of critical elements isobtained easily during assembly so that the manufacturing method lendsitself to mass production of the completed laser package. To bespecific, the ceramic element has dimensions of 0.520 inch by 0.516inch. The ceramic element encompasses an opening of 0.270 inch by 0.351inch. FIG. 3 shows the various elements to scale. A lid (not shown) isattached to the top of walls 11, 12, 13 and 14 once the subassembly issecured in place.

Electrical access, for power and control signals, is provided via pinouts 50 and 51 shown extending from wall 11 in FIG. 1. FIG. 4 shows anenlarged view of the pin out arrangement. The arrangement comprises aplanar ceramic element 53 which mates with a recess (not shown) in wall12. Element 53 includes spaced-apart holes 55 and 56 to whichelectrically-conductive pins are secured for insertion into a matingsocket to which power and control signals are applied. The pins areconnected electrically to lands 57 and 58 respectively (see FIG. 3).Signals and power are applied to the laser chip via wire lead pairs 61and 62 and 63 and 64 as shown in FIG. 3. A capacitor 65 (overlyingresistor 66) also is formed on the ceramic element. The operation of thelaser is analogous to that of commercially-available laser devices and,accordingly, is not discussed in detail herein. The present invention isdirected at an easily manufacturable laser package which relaxesalignment constraints and avoids misalignment of critical elementsduring any thermal excursions which might occur during operation.

FIG. 5 shows an alternative arrangement for the laser support 29 and thelaser device 28 of FIG. 2. Specifically, FIG. 5 shows first and secondlasers 80 and 81 on a support (or heat sink) 83. Laser 80 is mountedP-side down and is a qualified, good laser diode for later operation.Diode 81 is mounted P-side up (reversed) at the same time of assemblywhen the forward biased is assembled. The reversed diode is preferablyan optically impaired but electrically operative laser diodemanufactured at the same time as the good diode in order to exhibit likeelectrical characteristics. Diode 81 is used to provide a current pathfor any (reverse) currents generated during testing, power up, . . .etc. which otherwise might damage laser diode 80. The principal of theinvention can be applied to any arrangement of laser diodes as long asthe reversed diode is arranged in a electrically parallel fashion to theoperating good laser diode. As an example, for an array of laser diodesoperating in parallel in a single package a single reverse biased diodeis sufficient to protect all diodes during assembly and operation.

FIG. 6 shows the electrical circuit arrangement for the diodes 80 and81. The diodes are connected electrically in parallel across a voltagesource 85. The series arrangement of resistor 86 and capacitor 87 alsoare arranged in parallel and correspond to capacitor 65 and resistor 66of FIG. 3.

What is claimed is:
 1. A laser diode package including a first laserdiode having an emitting surface and a power source for applying avoltage to said diode for generating light from said emitting surface,said package also including a second diode connected electrically tosaid power source in parallel with said first laser diode and in adirection reversed from that of said first laser diode for providing apath for currents in said reversed direction which would otherwisedamage said first laser diode.
 2. A package as in claim 1 wherein saidsecond diode is a laser diode which is not operative optically but is anelectrically operative diode fabricated at the same time as said firstlaser diode so as to have electrical properties like those of said firstlaser diode.
 3. A package as in claim 1 also including an optical fiberhaving an end aligned with said emitting surface of said first laserdiode.
 4. A package as in claim 3 also including a cylindrical lensmounted between said emitting surface and said optical fiber.